Vascular access used in the treatment of patients involves central and peripheral vein accesses and arterial accesses. Catheterization of central veins is widely used in clinical practice; it is a necessary part of the treatment of patients in various settings. The most commonly involved vessels are the internal jugular, subclavian, and femoral veins. The mechanical, infectious, and thrombotic complications of central venous catheterization are markedly reduced when the procedure is performed with real-time ultrasound guidance or (to a slightly lesser extent) ultrasound assistance. Ultrasound guidance is also used to create peripheral venous accesses, for catheterization of peripheral veins and for peripheral insertion of central venous catheters. In this setting, it increases the catheterization success rate, especially during difficult procedures (e.g., obese patients, children) and reduces complications such as catheter-related infections and venous thrombosis. Arterial cannulation is used for invasive monitoring of arterial pressure and for access during diagnostic or therapeutic procedures. Ultrasound guidance reduces the risk of catheterization failure and complications. It is especially useful for arterial catheterization procedures performed in the absence of a palpable pulse (e.g., patient in shock, ECMO). Imaging support is being used increasingly to facilitate the creation of vascular accesses under difficult conditions, in part because of the growing use of ultrasonography as a bedside procedure. In clinical settings where patients are becoming increasingly vulnerable as a result of advanced age and/or complex disease, the possibility to reduce the risks associated with these invasive procedures should motivate clinicians to acquire the technical skills needed for routine use of sonographic support during vascular access procedures.